The present invention relates to a device for handling fuses and in particular, but not exclusively, to a device for safety inserting and extracting electrical fuses used in a three phase electrical fuse unit.
Fuse units are used in low voltage distribution and supply networks. Low voltage supply distribution from indoor and outdoor sub-stations include a fuse board, fuse pillar or fuse cabinet, incorporating a fuse unit, as part of the network and as appropriate to the particular application. Conventionally, four or five supply bus bars are provided, one for each of the three phases and either a common earth neutral bar or separate earth and neutral bars. Each three phase output taken from the supply has each power carrying cable connected to the bus bar of the respective phase by way of a fuse, the three fuses being mounted together in a fuse unit on a distribution unit. Each fuse is designed to engage and bridge a pair of contacts, one electrically connected to the respective bus bar, and the other to the respective output.
Two different types of fuse are used in such applications: UK style fuses with additional contact members and European style fuses. UK and European style fuses differ in their geometry and the contact members that they present to the pair of contacts in the fuse unit. UK style fuses have additional contact members providing a generally U shaped configuration and tend to be presented to contacts in a fuse holder in an inverted U manner with the contact members providing the legs of the U which engage the pair of contacts of the fuse holder. The legs of the U extend laterally to provide an extended region of contact between the fuse contact members and the fuse holder contacts adapted to receive them. European style fuses have fuse terminals providing integral flat planar contact members extending from either end of a main body and are inserted vertically into fuse unit contacts adapted to receive them.
In order to handle the supplied electrical currents and to provide good electrical and mechanical contact, the contact members of a European fuse are extended vertically. In contrast the contact members of UK style fuses extend laterally.
In order to allow for the safe handling of live fuses they must be rapidly and firmly inserted or removed form the live contacts. Owing to the U shaped configuration of UK style fuses this can be achieved quite readily. However, owing to the fact that European style fuses extend substantially further in the direction of their insertion or removal a greater stroke is required in order to safely effect their removal or insertion. European style fuses are becoming prevalent in a number of countries and the safety requirements for their handling are becoming more stringent. Hence there is a need for a device for effecting the safe handling of European style configured fuses in live fuse units.
European style configured fuse handling devices integral to a fuse unit can be provided but at increased cost and complexity to the fuse unit. A removable device suitable for use with a fuse unit allows the safe handling of all live fuses by a single device providing economies of cost and simplicity of fuse unit manufacture. A compact handling device is to be preferred, owing to the proximity of fuse units on fuse boards, pillars or cabinets and their ease of use by workmen.
According to a first aspect of the invention there is provided a fuse handling device for use with a fuse unit having a pair of contacts between which a fuse with integral switching contacts may extend in use, the handling device having an actuating lever operable into a first position and a second position, a charging means operably connected to the actuating lever and a drive means operably connected to the charging means, in which when the handling device in use is mounted on the fuse unit, the drive means attaches to the fuse and operation of the actuating lever into the first position charges the charging means to causes the drive means to extract the fuse from the pair of contacts and operation of the actuating lever into the second position charges the charging means to cause the drive means to insert the fuse into the pair of contacts, in which the fuse moves in a direction parallel to a plane defined by its switching contacts.
The device is for use in safely extracting and inserting European style configured fuses as used in fuse units. Both a European style fuse and a UK fuse without additional contact members, i.e. with integral fuse terminal/switching contacts, are considered to fall within the scope of a European style configured fuse. The invention allows fuses with integral switching contacts to be safely manipulated while the fuse unit is still live. The handling device is actuated by a throw lever. With the actuating lever in a first neutral position the device is mounted on a fuse unit and a drive means attaches to a fuse located between a pair of contacts in the fuse unit. Operation of the actuating lever into a first position charges up a charging means until sufficient energy has been stored to effect rapid and safe removal of the fuse from its pair of contacts. The device can also be used to safely insert a fuse between a pair of live contacts. The device with a fuse can be mounted on the live fuse unit and the actuating lever operated into a second position. Charging means are charged until sufficient energy is stored to effect the rapid and safe insertion of the fuse between a pair of contacts in the fuse unit. The device can move the fuse in a plane substantially parallel to the plane defined by the switching contacts of a European style configured fuse.
Preferably, the device has a housing and an axle extending across the housing and the actuating lever pivots about the axle. The provision of a housing improves the safety of the device and also provides a robust device capable of withstanding the mechanical forces exerted during extraction and insertion of a fuse.
The drive means of the device may include a member having a fuse engagement formation slidingly mounted on the device. The fuse engagement formation of the member securely attaches the fuse to the drive means for either insertion or extraction. Slidingly mounting the member on the device helps to robustly guide the motion of the fuse during extraction or insertion ensuring the fuse moves along a preferred path.
Preferably, the member slides in a direction parallel to a plank defined by the pair of contacts of the fuse unit. In this way frictional forces between the pair of contacts and the fuse are minimised and the fuse moves through the minimal possible distance thereby increasing the efficiency of the insertion of extraction of the fuse.
The charging means may include a pair of springs. The charging means may include two pairs of springs. Preferably, the springs of a pair of springs are wound in opposite senses.
An outer end of the first spring of the pair may be connected to the actuating lever and an outer end of the second spring of the pair may be connected to the drive means and the inner ends of the first and second springs are connected in series. This provides for charging the springs to a predetermined amount before they discharge to extract or insert the fuse. The predetermined amount should be sufficient to safely extract or insert a fuse in a live fuse unit.
Preferably the pair of springs are mounted concentric to the axle. In this manner the springs can be easily and simply operably connected to the actuating lever. The pair of springs may be connected in series via a square shaft mounted concentric to the axle.
Preferably a motion transformation device is mounted on the axle and engages the drive means. The motion transformation device can include members arranged to convert rotational motion to linear motion. The motion transformation device is preferably in the form of an arm which may be pivotally mounted on the axle and engage the drive means. In this way the rotational movement of the actuating lever and charging means may be transformed into linear movement of the drive means such that the fuse may be extracted or inserted sufficiently quickly so as to be achieved safely.
The housing of the device may have locating formations which when the device is in use co-operate with the fuse unit to locate the device. The locating formations ensure the correct registration of the device with respect to the fuse unit so that the fuse is extracted or inserted correctly and safely and also help prevent relative movement of the device and fuse unit during operation of the device.
According to a second aspect of the invention there is provided a fuse assembly having a fuse unit having a pair of contacts between which a fuse with integral switching contacts may extend in use and a fuse handling device having an actuating lever operable between a first position and a second position, a charging means operably connected to the actuating lever and a drive means operably connected to the charging means, in which when the handling device in use is mounted on the fuse unit, the drive means attaches to the fuse and operation of the actuating lever into the first position charges the charging means to cause the drive means to extract the fuse from the pair of contacts and operation of the actuating lever into the second position charges the charging to cause the drive means to insert the fuse into the pair of contacts, in which the fuse moves in a direction parallel to a plane of the switching contacts of the fuse.
The fuse unit may have three pairs of contacts between each of which a fuse with integral switching contacts may extend in use. In this way the assembly allows for the safe handling of European style configured fuses in a fuse unit handling a three-phase electrical supply.
Preferably, the pair of contacts define a plane and the device in use moves the fuse substantially parallel to the plane. In this way the safe extraction or insertion of the fuse is improved as the fuse is caused to move straight in or out of the contacts, reducing friction and electrical arcing.
The use assembly can include a fuse carrier interlock mechanism, the fuse having a carrier bearing an interlock formation on a side thereof, the fuse unit including an interlock mechanism including a projection directed toward the interlock formation, and engageable therewith to prevent motion of the fuse carrier relative to the fuse unit, and the handling device including an interlock actuating member which, in use, operates the interlock mechanism to disengage the projection and interlock formation so as to allow the fuse carrier to be extracted from or inserted into the fuse unit. In this way the fuse carrier is prevented from being removed from or inserted into the fuse unit without operation of the interlock mechanism.
A fuse handling device as claimed in claim 1 including a handling device interlock and for use with a fuse unit including a rear and a forward locating formation, the handling device including a notch engageable with the rear locating formation and a recess engageable with the forward locating formation, to allow the handling device to be slidably mounted on the fuse unit, and an interlock formation movable relative to the handling device and including a limb which when the forward locating formation is engaged in the recess is positionable between the rear and forward locating formations, to prevent relative sliding motion of the handling device and fuse unit thereby locking the handling device to the fuse unit. In this way registration of the handling device and fuse unit is ensured prior to operation of the device.
Preferably, the handling device includes an interlock lever on which the interlock formation is mounted so as to be movable between a locked and an unlocked position. More preferably, the interlock lever includes a part engageable with a part of the actuating lever to prevent operation of the actuating lever unless the interlock lever is in its locked position. In this way, the handling device is prevented from being mounted on or removed from the fuse unit, unless the handling device is in a non-operating configuration. Most preferably, the interlock lever part is a notch and the actuating lever part is a member extending parallel to the pivot axis of the actuating lever.
The fuse handling device can include a locking mechanism for use with a fuse carrier having a fuse carrier locking formation, the handling device including a pivotable arm with a notch at a free end which in use is engageable with the fuse carrier locking formation so as to selectively lock the fuse carrier to the fuse handling device, a cam drivable by the actuating lever and acting on the pivotable arm such that when the actuating lever is in a neutral position, the arm cannot pivot thereby locking the fuse carrier to the fuse handler. In this way, the fuse carrier is safely locked in the handling device prior to insertion or after removal from the fuse unit.
The fuse handling device can include resilient biassing means which biases the pivotable arm into a locking position.
The cam can include a first part and a second part which when driven by the actuating lever to act on the pivotable arm allow the arm to pivot thereby allowing engagement or disengagement of the notch and locking formation.